Electrocardiograph electrodes with surface convexities



April 14, 1970 D. s. LEWES ET AL 3,505,993

ELECTROCARDIOGRAPH ELECTRODES WITH SURFACE CONVEXITIES Filed Dec. 17,1965 FIG. 7.

o o o 0 5 61- o 0 0 o o F162. 3 2 7 OZ United States Patent US. Cl.128.-2.06 3 Claims ABSTRACT OF THE DISCLOSURE An electrocardiographelectrode having a form such that skin preparation prior to applicationof the electrode can be dispensed with in most cases. The electrodecomprises :a rigid metal sheet applied to the skin and making with it amultiplicity of small area contacts by means of points or edges whichare distributed uniformly over the area of application and which pressinto the skin without penetrating 'beyond the epidermis.

This invention relates to electrodes for making electrical contact tothe living body of a person, and is particularly concerned withelectrodes for use in electrocardiography.

In electrocardiography the condition of the heart of a human subject (orof an animal in Veterinary practice) 'is investigated by makingrecordings of electrical signals generated in the body of the subject asa result of the heart beat. In order to pick up the electrical signalsit is necessary to make satisfactory electrical contacts with the bodysurface at appropriate locations, and forthis purpose it is the normalpractice to use skin contact electrodes. Such an electrode comprises ametallic member, so shaped that it may be brought into contact over anappreciable and appropriate skin area, and which is provided with aterminal for making connection to a lead extending from the recordinginstrument; hitherto such electrodes have been provided with smoothcontact surfaces, and in some cases the contact surf ce is covered witha cloth impregnated with saline solution or alcohol. Two types ofelectrode are in normal use, one having a fiat or concave contactsurface suitable for application to the limbs and the other having aflat contact surface or a circular contact ring in the form of a hollowmetal cone suitable for application to the chest; in use the limbelectrode is maintained in position by a perforated rubber band ornylon-grip cloth encircling the limb and passing over or attached to theelectrode, or by a spring clip attachment, while the chest electrode ismaintained in position by a suction device or by a rubber bandencircling the chest.

When using conventional skin contact electrodes with modernelectrocardiographs it is necessary, if satisfactory recordings are tobe obtained Without appreciable delay after the applictaion of theelectrodes, to carry out preliminary skin preparation at the relevantlocations in order to reduce the natural skin resistance; for thispurpose it is still common practice to use a substance known aselectrode jelly, which contains both an electrolyte (usually in highconcentration) and a finely divided abrasive. The use of electrode jellyis time-consuming and inconvenient, and could in fact cause fatal delayin certain cardiac emergencies (for example in clinical arrest of theheart from coronary thrombosis, where the time factor is vital and anelectrocardiogram is essential to decide upon appropriate treatment).Further disadvantages of the use of electrode jelly are that it iscostly, it may be aesthetically repugnant from the point of view of asubject, and it eventually results in some degree of corrosion of themetallic electrodes and apparatus and leads to premature deteriorationof associated rubber bands due to the necessary frequent cleansing.

It is therefore an object of the present invention to provide electrodeshaving a form such that the need for preliminary skin preparation can beavoided in most cases.

In its broadest aspect the present invention provides anelectrocardiograph electrode, comprising a metallic structure providedwith a terminal for making connection to a lead and shaped so that itmay be applied to the skin of the body over an appreciable area, themetallic structure having a multiplicity of convexities disposed andshaped so that when the structure is appropriately applied to the skinand held firmly in contact the convexities will press into the skinwithout penetrating beyond the epidermis.

In one form of electrode according to the invention, the convexities areconstituted by small pointed projections distributed over the surfacearea which is to be applied to the skin. It has been found that by usingelectrodes of this form it is possible in most cases (including those inwhom the limbs are hairy or the skin is unnaturally dry) to obtainsatisfactory electrocardiograms without appreciable delay after theapplication of the electrodes and without any preliminary skinpreparation. Such electrocardiograms are strictly comparable with thoseobtained in the same subject using conventional electrodes and electrodejelly. Controlled observations on which the invention is based have beencarried out primarily with electrocardiographs having high inputimpedances (of the order of several megohms) but it has been shown bycontrolled experiment that lim-b electrodes provided with small pointedprojections could equally well be used with recording instruments oflower input impedance, including the string galvanometer of relativelyvery low impedance (2,0003,000 ohms). It would appear that the efiicacyof the pointed projections results from their penetrating through thesuperficial insulating layer of the skin (the stratum corneum) whichcontributes the major part of the natural skin resistance, therebymaking intimate contact at a number of points with the underlying layerof the epidermis. It will of course be appreciated that the form anddistribution of the projections should be such that the penetration ofthe skin is insuflicient to cause any substantial discomfort or injuryto the subject when the electrode is applied. An arrangement utilisingprojections of length 1.5 mm. distributed 36 to each square cm. of thecontact area has been found suitable, provided that care is taken not toapply the electrode in the region of a superficial -bony prominence; itis not thought that these figures are particularly critical. Firm butuniform pressure of the electrode upon the skin surface is important forensuring intimate skin contact.

In an alternative form of electrode according to the invention theconvexities are constituted by the edges of small holes distributed overthe surface area which is to be applied to the skin, means beingprovided for applying suction to the skin via the holes. In this case itwould appear that there is no complete penetration of the stratumcorneum, but the drawing of the skin surface into the holes as a resultof the suction causes the skin to be stretched around the edges of theholes so that at these edges the stratum corneum is appreciably thinned,with a consequent improvement in electrical contact with the epidermis.The holes may suitably be of circular form with a diameter of the orderof one mm., and may be distributed about 25 to each square cm. of thecontact area.

Various illustrative embodiments of the invention will now be describedwith reference to the accompanying drawings in which:

FIGURE 1 is a side view of an electrode suitable for application to ahuman limb;

FIGURE 2 is an underneath plan view of the electrode in FIGURE 1;

FIGURE 3 is a sectional view of one form of electrode suitable forapplictaion to the human chest; and

FIGURE 4 is a sectional view of a second form of electrode suitable forapplication to the human chest.

The electrode shown in FIGURES 1 and 2 comprises a stainless steel sheet1 which is curved to have the form of a portion of a cylinder and whichhas formed integral with it an outwardly projecting tongue 2 whose freeend is curled round so as to constitute a socket suitable for receivinga plug (not shown) attached to an electrocardiograph lead. The sheet 1is of similar form to a conventional limb electrode and may suitablyhave a radius of curvature of 4 cms., and a surface area for each mainface of 30 square cms. To the concave face of the sheet 1 is secured(for example, by soldering, welding or rivetting) a thin metal sheet 3which is bent to conform to the curvature of the sheet 1 and which hasbeen perforated by a series of uniformly distributed holes so formed asto leave a small number of triangular teeth 4 projecting from theperiphery of each hole in a direction perpendicular to the surface ofthe sheet 3, the sheet 3 being secured to the sheet 1 so that the teeth4 project on the side of the sheet 3 remote from the sheet 1. Suitablematerials for the sheet 3 are tin-plated soft iron and the alloy knownas German silver and a suitable arrangement for the holes is to havenine holes per square cm., each hole having a diameter of two mms. andproviding four teeth which project 1.5 mm. from the general surface ofthe sheet 3.

In use the electrode is applied to a fleshy part of the forearm or lowerleg so that the teeth 4 press into the skin, the electrode being heldfirmly in position by a rubber band (not shown) encircling the limb andpassing over the electrode, the band being provided with slots whichengage with the tongue 2.

Turning now to FIGURE 3, the electrode shown therein comprises a metaldisc 5 to one main face of which is secured a circular metal sheet 6which has been perforated in a similar manner to the sheet 3 to provideteeth 7 projecting from the sheet 6 on the opposite side to the disc 5.The sheet 6 may suitably have a diameter of 2.5 cms., and from the pointof view of efliciency in overcoming natural skin resistance it may bedesirable to provide a somewhat larger number of teeth per unit area inthis case than is the case for the sheet 3, it being relevant in thisconnection that the skin contact area must necessarily be confined inchest lead electrocardiography (in contrast to limb leadelectrocardiography in which the skin contact area is relativelyunimportant). The disc 5 is formed integral with a hollow boss 8 whichprojects from the main face of the disc 5 opposite the sheet 6, the boss8 being internally threaded and screwing on to a threaded portion of aterminal post 9 in which is formed a circular hole 10 adapted to receivea plug (not shown).

The terminal post 9 extends perpendicularly through the base of acircular cylindrical cup 11 of insulating material so that the disc 5and sheet 6 are disposed within the cup 11 with the points of the teeth7 slightly recessed with respect to the rim of the cup 11, the terminalpost 9 being secured in position with a nut 12. The cup 11 has a sidetube 13 which is connected by flexible tubing 14- to a conventionalexhausting bulb 15.

In use of the electrode, the cup 11 is applied so that the whole of itsrim is in contact with the chest, and suction is applied to the interiorof the cup 11 by operating the bulb 15 so that the cup 11 is firmly heldin place and the skin is drawn into contact with the points of the teeth7. Slight complication may arise where the electrode is applied to asubject who is particularly hirsute or has a particularly dry skin,since in these cases it may be difficult to obtain adequate suction tomaintain the electrode firmly in contact with the skin; the diflicultymay be overcome in the first case either by applying to the skin aninocuous abrasive-free lubricating jelly of low electrolyte content orby shaving the relevant parts of the chest, and in the second case bymoistening the skin with a damp sponge.

Turning now to FIGURE 4, the electrode shown therein comprises acylindrical metal chamber 16 constituted by a cup 17 and a cover plate18 secured to the cup 17, the plate 18 being provided with a tag 19 towhich is soldered one end of an insulated lead 20 whose other end isconnected to a terminal 21 providing a socket adapted to receive a plug(not shown). The base of the cup 17 is perforated cleanly with a regulararray of small holes 22, and is provided with a projecting circular rim23 which surrounds the perforated area. The cup 16 may suitably have anexternal diameter of about 3.5 cms., the base of the cup 17 having athickness of one mm. and being perforated with circular holes ofdiameter one mm. distributed 25 per square cm. over a central circulararea of diameter 2.5 cms.; the material of the cup 17 may again suitablybe tin-plated soft iron or German silver. The plate 18 is provided witha tube 24 connected by flexible tubing 25 to an exhausting bulb 26.

In use the electrode is applied so that the whole of the rim 23 is incontact with the chest, and suction is then applied to the interior ofthe chamber 16 by operating the bulb 26 so that the electrode is held inposition and the skin is drawn into contact with the exterior of thebase of the cup 17 and partially into the holes 22. In some cases,particularly with hirsute subjects, it may be desirable to provideauxiliary means to assist in producing the necessary suction to hold theelectrode firmly in position. This auxiliary means may take the form ofan annular sheet of flexible material (not shown) whose inner part issecured to the electrode, for example being clamped between the cup 17and the plate 18, and whose outer part bears against the chest aroundthe electrode.

It will of course be appreciated that many alternative embodiments ofthe invention are possible. For example an electrode similar in form tothe one shown in FIG- URES l and 2 could be provided with a spring clipdevice for maintaining it in position. Further, electrodes comprising aperforated sheet-like member similar to the base of the cup 17 in theelectrode shown in FIG- URE 4 may have the contact surface curvedinstead of flat, and may be arranged to be maintained in position bymeans other than the suction device provided for drawing the skin intothe holes.

We claim:

1, An electrocardiograph electrode comprising:

a metallic structure provided with a terminal for making connection to alead and incorporating a rigid sheetlike member shaped so that it may beapplied to the skin of a subject over an appreciable area,

said member being formed so as to present to the skin a multipuicity ofsimilar small convexities distributed in a substantially uniform patternover the area applied to the skin,

the said convexities being disposed and shaped so that when said memberis appropriately applied to the skin and held firmly in contact theconvexities will press into the skin without penetrating beyond theepidermis,

said convexities being constituted by the edges af small holes formed inthe sheet-like member, and

means being provided for applying suction to the skin via the holes.

2. An electrocardiograph electrode comprising:

a metallic structure provided with a terminal for male ing connection toa lead and incorporating a rigid sheet-like member shaped so that it maybe applied to the skin of a subject over an appreciable area,

said member being formed so as to present to the skin a multiplicity ofsimilar small convexities distributed in a substantially uniform patternover the area applied to the skin wherein the convexities areconstituted by small pointed projections in the form of triangular teethformed by perforating the sheet-like member and extending outwardly fromone main face of the sheet-like member,

the said convexities being disposed and shaped so that when said memberis appropriately applied to the skin and held firmly in contact theconvexities will press into the skin without penetrating beyond theepidermis.

3. An electrocardiograph electrode comprising:

a metallic structure provided with a terminal for making connections toa lead and incorporating a rigid sheet-like member shaped so that it maybe applied to the skin of the subject over an appreciable area,

said member being formed so as to present to the skin a multiplicity ofsimilar small convexities distributed in a substantially uniform patternover the area applied to the skin wherein the convexities areconstituted by the edges of small holes formed in the sheetlike member,

the said convexities being disposed and shaped so that when said memberis appropriately applied to the skin and held firmly in contact theconvexities will press into the skin Without penetrating beyond theepidermis,

means being provided for applying suction to the skin via the holes, and

said metallic structure including a chamber to which suction may beapplied, the chamber having a perforated Wall which constitutes saidsheet-like member.

References Cited UNITED STATES PATENTS 872,688 1'2/ 1970 Saighrnan128-417 X 1,889,271 11/1932 Zevne 128-416 1,935,138 11/1933 Windisch128-418 X 2,580,628 1/ 1952 Welsh 128-404 2,660,175 11/1953 Thrasher eta1. 128-404 3,067,749 12/1962 Walters 128-418 3,295,515 l/1967 Kahn128-206 WILLIAM E. KAMM, Primary Examiner

